We previously demonstrated that ovomucoid, Gal d 1, is the dominant allergen in hen's egg. Ovomucoid is a highly glycosylated protein comprised of 186 amino acids arranged in 3 tandem domains [Gal d 1.1, 1.2, 1.3], each about 60 amino acids in length. The purpose of this study was to evaluate the allergenic properties of ovomucoid. We isolated the 3 ovomucoid domains by enzymatic digestion and chromatographic purification. Sera from 45 egg allergic patients with atoppic dermatitis were anlyzed by ELISA to determine B cell domain specificity; sera from egg allergic patients were analyzed by inhibition-ELISA to reduce and alkylated, oxidized, and deglycosylated ovomucoid in order to evaluate the importance of linear and conformational structures, and carbohydrate to B cell epitopes. Peripheral blood T cells from 13 egg allergic patients were used to evaluate T-dominant domains and reactivity to reduced and oxidized ovomucoid. Virtually all patients had IgE antibodies to the 3 domains, although there was significalty more IgE activity to Gal d 1.2 [percentage of ovomucoid- specific IgE; median: Gal d 1.2: 40%; Gal d 1.1:23%; Gal d 1.3 26%]. Quantities of patient IgG antibody was comparable to all 3 domains. IgE antibody binding to reduced ovomucoid and IgG binding to oxidized ovomucoid were significantly reduced compared to native ovomucoid [28% and 69%, respectively]. Twenty-one of 33 peripheral blood T cells reacted to Gal d 1.3, 18 of 33 to Gal d 1.2, and 18 of 33 to Gal d 1.1. T cell proliferation in vitro to reduced and oxidized ovomucoid were significantly greater than to the native protein. These results indicate a dichotomy between T cell and B cell comain dominance, and differences in IgE and IgG epitopes. Furthermore results suggest that conformational B cell epitopes play a more significant role in ovomucoid allergenicity in some patients, especially those with "transient" egg hypersensitivity than previously appreciated, and that carbohydrate moieties have a minor effect on allergenicity.